This is quite a useful rule when you think about it, because it prevents anyone from being tricked into trading a rare card for a common one
As one of the final Sword & Shield expansions, sealed products benefit from scarcity and nostalgia
It requires building around since you can only cast it from your graveyard, not your hand, so cards like Entomb / Jarad's Orders / Wargate are needed, but it's worth it: with Haakon on the battlefield, not only can you cast any Knights from your graveyard like Knight Exemplar or changelings like Mirror Entity, but Haakon can also cast tribal instants like Crib Swap to repeatedly exile threats or Blades of Velis Vel, which together with The Ur-Dragon and Morophon, the Boundless lets you cast Blades infinite times for infinite power
Then when this swings you can trade a Food for milling three and putting a permanent from them to your hand
Green is the color of ramp, and you could easily cast this on turn six and then break the game